Patent GB-989281-A (GB)
Title: Improvements in or relating to hydraulic brake operating cylinders
IPC: F16D65/22
Filed: 1964-03-19
Abstract: 989,281. Hydraulic brakes. FRANCAISE DU FERODO S.A. March 19, 1964 [March 26, 1963], No. 11742/64. Headings F2E and F2F. A master cylinder for hydraulic brakes has a piston unit 14 which forms two primary chambers 19, 21 whence it drives equal or proportional volumes into the primary circuits 78, 80 of two brakes 70, 71 and a secondary chamber 20 which is connected to a circuit 82, 83, 84 balancing the reactions of the two brakes, the secondary chamber being reduced in volume by depression of the piston 14 and is characterized by provision of means for selectively controlling the pressure in the secondary chamber 20 so as to avoid excessive effort in depressing the said piston unit. The master cylinder is of the kind described in Specification 846,055 with the secondary chamber (not shown in Fig. 1) aligned between the two others, each chamber co-operating with one of three pistons on the single spool 14 which is moved by a pedal 15 against the force of a return spring in the chamber 19. Below the chamber 20 is a safety chamber 38, seen in transverse section in Fig. 4, which is subject to pressures from a piston at either end, the pistons themselves being subject to the pressures in the chambers 19 and 21 respectively (vide Specification 846,005). The secondary circuits 84 and 89 are connected to the chambers 20 and 38 through plugs 44 and 45. A piston 47 having a large diameter head is located in a bore 46 adjoining the chamber 20 and its smaller diameter tail 48 is in a bore 49 in the plug 44. A valve element 50 on the end of the piston 47 bears on a seating 51 to form a valve which controls connection between the chamber 20 and a tank 22 through a bore 53 in the piston. A ring 54 slides on the tail 48 and is urged against a seating 55 by a spring 56. A chamber 65 in the plug 43 connects with the chamber 20 through a valve 63 and a stop-lamp switch 67 screws into its outer end. The chamber 38 connects at 66 with the chamber 65 and at 58 with a space 59 in the plug 44. When pedal 15 is depressed chambers 19 and 20 deliver equal volumes through primary conduits 78 and 80 to cylinders 74 and 76 of the front brakes 70 and 71. An additional volume from chamber 20 lifts valve 64 and passes through conduits 87, 88 and 89 to cylinders 85, 86 of rear brakes 72, 73; it also passes by way of 66-38-58 and a small calibrated hole 60 through conduits 82, 83 and 84 to cylinders 75 and 77 of the front brakes. After the front brakes have made contact the secondary pressure rises rapidly and passes by way of 82-83-84-61-60-58-38 and 66 to close valve 64 so as to isolate the chamber 20. This pressure also moves the piston 47 to open valve 50,51 to the tank 22 so that further pressure on the spindle 14 does not give rise to undue effort when increased braking is required. During this stage the two pistons in the chamber 38 (Fig. 2, not shown) act if required to equalize the primary pressures and to serve as a safety device in event of a rupture of the secondary circuits. If the brake pedal 15 is depressed several times with a pumping action with the valve 50, 51 closed, when the pressure in the chamber 20 reaches the calibration pressure of the spring 56 the piston 47 moves towards the left and again opens the valve 50, 51 so that an excessive back pressure is not built up. In Fig. 5 an arrangement is illustrated similar to that already described but which attenuates the excess pressure by means of a stepped piston 94. Figs. 6 and 7 (not shown) illustrate an embodiment in which the stepped piston 94 is arranged in the chamber 38 in place of the two pistons previously mentioned. Fig. 9 illustrates a diaphragm device 104 for vacuum-assisted brake systems wherein, if there is a failure in the vacuum line 102, a spring 106 causes a diaphragm 104 to actuate a plunger 105, tilting a valve 24 whereby the chamber 20 is opened to the reservoir 22 to reduce the effort needed for application of the brakes by manual force alone.